The present invention relates to frangible metal articles, and, in particular, to frangible bullets having particular use in target and/or training applications. Indoor and outdoor shooting applications benefit from the absence of lead as well as the frangibility (break-up) characteristics. Frangible bullets for such uses are well known. They are characterized by the use of metal powder consolidated into a bullet that has sufficient strength to maintain its integrity during firing while fragmenting on impact with a solid object having sufficient mass and rigidity to fracture the bullet.
Conventional, full-density, cast, swaged, copper plated or copper jacketed lead bullets are also used in indoor firing ranges and for training. In order to protect the shooters from ricochets, a "bullet trap" is normally required to stop the projectile and any resulting fragments from injuring shooters. Furthermore, the walls of the firing range or training facility may be covered with rubber or some other projectile absorbing material to stop occasional ricocheting bullet fragments. Thus, the cost of constructing and maintaining indoor target/training ranges is substantial. Moreover, even using bullet traps and ricochet absorbing materials on the walls, occasionally a ricochet will somehow defeat such systems and injure a shooter.
Shooting lead bullets causes the emission of airborne lead dust that is introduced into the atmosphere. This requires the implementation of elaborate ventilation systems and may require individuals working in such facilities to undergo blood monitoring programs to determine the amount of lead in their bloodstream. The accumulation of spent lead bullets and bullet fragments must be properly disposed of and regulations concerning the disposal of lead waste are becoming increasingly complex. Thus, the generation of lead dust and the accumulation of spent lead bullets and fragments causes environmental concerns and poses the potential for serious health problems.
There has been a long-standing search for a material to use as a bullet that does not contain lead. One problem in replacing lead in ammunition is that the replacement material must be sufficiently heavy such that ammunition using such bullets, when used in automatic or semi-automatic weapons, will be able to cycle the weapon properly.
The main criteria for the ability of a round to cycle automatic or semi-automatic weapons is the amount of energy that the ammunition delivers to the cycling mechanism. For some types of weapons, this energy is delivered by the expanding gases pushing back the cartridge case. For some others, the recoil is used and for still others high-pressure gases are connected, through a port inside the barrel, to a mechanism that cycles the firearm.
All firearms, are designed to function with bullets and propellants (gunpowder) that produce certain pressure-vs-time characteristics. Using a lighter bullet may cause problems in operation of a semi-automatic or automatic weapon if there is too low an energy transfer to give the mechanism the needed energy to cycle. While the energy can be increased by the use of additional propellant or different types of propellants, this is not desirable because the characteristics of such a training round would be significantly different from the ammunition having conventional bullets and propellants.
In addition, in order to replace lead in a bullet, the selected material should have a large enough specific gravity so that the resulting bullet mass is compatible with commercially available propellants. It is not economically feasible to develop a lead-free round where a special propellant or other component would need to be developed.
Further, a lead-free, training round should break up into small particles when it hits a hard surface. The individual particles are then too light to carry enough energy to be dangerous. On the other hand, such bullets should be sufficiently strong to withstand the high accelerations that occur on firing, ductile enough to engage the barrel rifling and durable enough to retain the identifying engraving from the rifling as required by government agencies.
Practice and training rounds employing combinations of resinous binders and metallic powders have generally not proven satisfactory because of uncontrollable frangibility characteristics, insufficient strength, increased fouling of the barrel of the weapon, decreased barrel longevity and inability to retain or receive engraving from the rifling of the barrel through which it is fired.